A work machine, such as an agricultural work machine, a construction work machine or a forestry work machine, typically includes a power unit in the form of an internal combustion (IC) engine. The IC engine may either be in the form of a compression ignition engine (i.e., diesel engine) or a spark ignition engine (i.e., gasoline engine). For most heavy work machines, the power unit is in the form of a diesel engine having better lugging, pull-down and torque characteristics for associated work operations.
The step load response of an IC engine in transient after a load impact is a feature mostly influenced by the engine displacement, the hardware of the engine (e.g., whether it has a standard turbocharger, a turbocharger with waste gate or variable geometry, etc.), and by the software strategy for driving the air and fuel actuators (e.g., exhaust gas recirculation, turbocharger with variable geometry turbine (VGT), fuel injector configuration, etc.) with respect to the requirements of emissions legislation (e.g., visible smoke, nitrous oxides (NOx), etc.), noise or vibrations. The load impact may be the result of a drivetrain load (e.g., an implement towed behind the work machine) or an external load (i.e., a non-drivetrain load). External loads can be classified as including both parasitic and auxiliary loads. Parasitic loads are non-drivetrain loads placed upon an engine through normal operation of the work machine, without operator intervention (e.g., an engine cooling fan, hydraulic oil cooling circuit pump, etc.). Auxiliary loads are non-drivetrain loads placed upon an engine through selective operator intervention (e.g., an auxiliary hydraulic load such as an unloading auger on a combine, a front end loader, a backhoe attachment, etc.)
Engine systems as a whole react in a linear manner during the application of a transient load. Initially, the load is applied to the drive shaft of the IC engine. The IC engine speed decreases when the load increases. The engine speed drop is influenced by whether the governor is isochronous or has a speed droop. The air flow is increased to provide additional air to the IC engine by modifying the air actuators. A time delay is necessary to achieve the new air flow set point. The fuel injection quantity, which is nearly immediate, is increased with respect to both the smoke limit and maximum allowable fuel quantity. The engine then recovers to the engine speed set point. The parameters associated with an engine step load response in transient after a load impact are the speed drop and the time to recover to the engine set point.
An IC engine may be coupled with an infinitely variable transmission (IVT) which provides continuous variable output speed from 0 to maximum in a stepless fashion. An IVT typically includes hydrostatic and mechanical gearing components. The hydrostatic components convert rotating shaft power to hydraulic flow and vice versa. The power flow through an IVT can be through the hydrostatic components only, through the mechanical components only, or through a combination of both depending on the design and output speed.
A work machine including an IC engine coupled with an IVT may exhibit problems to be overcome in two ways: First, sudden loads placed on the drivetrain or vehicle hydraulic functions cause the engine speed to decrease. The response time to change the IVT ratio to reduce engine load once decreased is slower than necessary to prevent substantial engine speed drop and sometimes stall. Second, when an external load is applied to the IC engine, such as when filling the bucket of a front end loader on an IVT vehicle, the operator may command a vehicle speed substantially more than what is capable from the IC engine. Under these conditions the IVT output torque and speed may result in excessive wheel slippage and other undesirable characteristics. Likewise, if an external load from another external function to the transmission is activated, such as hydraulic functions, the external load combined with the transmission output capability may place the engine in an overload condition.
The demands for increased performance and fuel economy will increase significantly for farm machinery within the next decade. For combines, the need to improve productivity will be compounded by the addition of other functional capabilities beyond merely the threshing and cleaning of grain. The advent of attachments for biomass collection, stalk chopping for residue management and fine cut straw choppers are some examples of using the combine to not only collect grain, but to also collect residue for ethanol refining or chop up residue for better reincorporation of plant nutrients in the soil. These functions require significant amounts of engine power beyond the traditional harvesting function. Because levels of engine output in the tier 4 (T4) timeframe will be limited, other ways of delivering increased performance, features and fuel economy will be required in order to provide adequate power for these additional functions.
Currently, for cornheads with integral stalk chopping capability, a higher horsepower torque curve is automatically selected by the engine control unit (ECU). This causes the IC engine to generate more power to offset the increased power demand to enable the stalk chopping function. This is called “intelligent power management” or IPM. Essentially, the engine power output is automatically controlled to deliver just the amount needed to meet the load as a function of all of the various threshing, propulsion, and residue chopping required. IPM enables the operator to configure the combine with the appropriate header either with or without stalk chopping and the powertrain automatically selects the proper torque curve to provide enough power to provide consistent, predictable performance and for good fuel economy. A higher power output can be selected for high power needs or a lower curve for non-chopping situations, without noticeable differences in machine throughput capability. Fuel consumption can be saved with the lower curve, if the operator is not chopping.
The basic problem is that the power output of currently available IC engines is limited. As combines get larger and as additional functions such as biomass collection are added, there will not be enough power from the IC engine and a higher torque curve cannot be selected as a result. Invariably, combine performance will be limited in this situation.
What is needed in the art is an agricultural harvester and corresponding method of operation providing sustained, increased power capability for carrying out additional functions during a harvesting operation.